public class CopyAttachmentHandler {
    public static void copyAtt(List<ProjectDemo__c>pdList){
        try{
            
            //releted opp id
            Set<ID> OppId = new Set<ID>();
            Set<ID> CdId = new Set<ID>();
            
            // related attachment id of opp id
            Set<ID> attId = new Set<ID>();    
            
            for(ProjectDemo__c pd1:pdList){
                OppId.add(pd1.Opportunity_Name__c);
            }
            System.debug('@@@@@@ oppid'+OppId);
            
            for(ContentDocumentLink ac:[SELECT Id,ContentDocumentId FROM ContentDocumentLink WHERE LinkedEntityId IN:OppId]){
                attId.add(ac.Id);
                CdId.add(ac.ContentDocumentId);
            }
            System.debug('@@@@@@ Attid'+attId);
             System.debug('@@@@@@ CdId'+CdId);
            
            list<ContentVersion> newContentVersion=new list<ContentVersion>();
            list<ContentDocumentLink> cdl=new list<ContentDocumentLink>();
            
            List<ContentVersion> attachmentList = [SELECT Id, VersionData,Description, Title, ContentBodyId, ContentDocumentId FROM ContentVersion WHERE ContentDocumentId IN:CdId];
            System.debug('@@@@@@ attachmentList'+attachmentList);  
            
        
            for(ContentVersion att: attachmentList) {
                ContentVersion newFile = new ContentVersion();
                newFile.Title = att.Title; 
                newFile.ContentBodyId = att.ContentBodyId;
               
                newFile.Description=att.Description;
                newContentVersion.add(newFile);
            }
            insert newContentVersion;
            
            
           List<Id> CdIdid = new List<Id>();
            
            for(ContentVersion cvv:newContentVersion){
                CdIdid.add(cvv.ContentDocumentId);
            }
             System.debug('@@@@@@ new content documnet id'+CdIdid);  
            
          
            for(ProjectDemo__c pd:pdList){
                ContentDocumentLink newLink= new ContentDocumentLink();
                newLink.LinkedEntityId=pd.Id;
                for(Id ccd:CdIdid){
                    newLink.ContentDocumentId=ccd;
                }
                cdl.add(newLink);  
            }
            insert cdl;
            
               
        }
        catch(Exception e){
            system.debug('@@@@ Error'+e);
        }
        
        
    }
    
}